Estimating solar radiation on slopes of arbitrary aspect

Solar radiation is a major environmental factor, controlling for example, plant growth, inactivation of fecal microbial contaminants, and soil property evolution. Modeling the magnitude and complexity of changes in solar radiation under cloudy conditions is a challenge. In this paper, we present a simple approach for estimating daily global solar radiation on any sloping surface with arbitrary aspect given global radiation data for nearby flat terrain. The system is a further development of existing models and consists of two parts. The first part estimates direct and diffuse components of solar radiation from measured global radiation for a horizontal surface. The second part uses separate estimates of direct and diffuse radiation to calculate the daily global radiation throughout the year on slopes of different steepness and aspect. The performance of the system was verified with solar radiation data on various slopes and aspects at latitude 37.8°S in New Zealand.